Postoperative Polyuria: What It Is, Why It Happens, and What to Do

When you hear postoperative polyuria, the condition of producing abnormally large amounts of urine after surgery. Also known as surgical diuresis, it’s not always a problem—but it can be a red flag if ignored. Many people leave the hospital thinking they’re fine because they’re urinating, but too much urine can mean your body is losing more than just water—it’s losing electrolytes, sodium, even kidney function control. This isn’t rare. In fact, up to 30% of patients who’ve had major surgery, especially those on IV fluids or certain meds, experience it.

It often shows up 12 to 48 hours after surgery. Your kidneys, stressed from anesthesia, pain meds, or blood loss, suddenly switch from holding onto fluid to flushing everything out. That’s when you start going to the bathroom every hour, or worse—waking up soaked at night. The real danger isn’t the peeing itself. It’s what’s missing from your blood: low sodium, low potassium, or even low blood pressure from dehydration. Fluid balance, the delicate equilibrium between how much fluid you take in and how much you lose is everything here. And urine output, the exact amount of urine your body produces over time is the number your nurses track hourly in recovery. If it’s over 200 mL per hour for several hours, that’s not normal. That’s a signal.

Some causes are straightforward. You got a ton of IV fluids during surgery. You stopped taking blood pressure meds that kept you retaining fluid. You had a kidney transplant or brain surgery—both can trigger sudden diuresis. But other times, it’s a side effect of meds like mannitol or furosemide, or even a sign of uncontrolled diabetes that flared up under stress. The trick is figuring out which one it is. That’s why your care team checks your blood, your weight, your sodium levels, and your urine concentration. It’s not just about counting how many times you’ve been to the bathroom.

What you’ll find in the posts below isn’t a textbook on kidney function. It’s real, practical info from people who’ve been through this—what worked, what didn’t, what their nurses missed, and how to spot trouble before it becomes an emergency. You’ll see how postoperative polyuria connects to other recovery issues: fluid shifts after heart surgery, how pain meds affect your kidneys, why some people crash after being discharged because nobody checked their sodium. These aren’t just stories. They’re checklists you can use.